Cyaniding process



L. D. MILLS AND T. B. CROWE.

CYANIDING PROCESS.

APPLICATION FILED MAR.21.1918.

Patented Aug. 9, 1921.

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`Mrap STATES. PATENT-OFFICE- LO-'UIS D. MILLS, OF SAN FRANCISCO, CALIFORNIA, AND'HOMAS ASSIGNORS TO THE MERRILL COMPANY, CISCO, CALIFORNIA, A. CORPORATION 0Fr CALIFORNIA..

VICTOR, COLORADO,

n. cRoWE, vor or SAN FRAN- cYAmnINe PROCESS.

To all whom t may concern.'

Be it known that we, LOUIS D. MILLS, a citizen of the United States, residing at San Francisco, in thecounty of San Francisco and State of California, and THQMAS B. Crown, a citizen of the United States, residing at Victor, Teller county, Colorado, have invented certain new ments in Cyaniding Processes, of which the following is aspecification. .d

rlhe invention relates to a process for recovering cyanogen and represents lmprovements in cyaniding processes. The objects of the invention are to. diminish cyaniding, increase` its eiiiciency, extend its application, and render applicable the combination of it with other processes inthe treatment of sundry complex ores.

Heretofore, in cyanidlng processes the metal has been dissolved in a solution con-A taining a protective excess of alkali, saidexcess varying in amount in accordance with `the character of the metal, and the metal has been recovered from the solution by the addition thereto lof a precipitant, as, for instance, zinc dust, The processes as practised have-resulted in loss of much cyanogen and the practice of cyaniding has, accord ingl been expensive and practically limited to t e recovery of recious metals. An important feature of t e present invention consists in the recovery of the cyanogen or material parts thereof in 'such manner as to secure advantages indicated in the follow ing description of the preferred embodiment, which description embraces more than will be used in many instances of actual practice and admits of much variation according to the materialto be treated and the circumstances presented in particular Cases.

The means and methods of bringing the metal into solution in cyanid. solution are too well known to require particular description. But it may be observed that the present invention renders practicable the use of stronger solutions, particularly in treatin silver ores, thus promoting greater and quicker recovery of the metal. Followin any available practice of bringin the meta into solution and in most, thoug not necessarily all, instances after the solution has been separated from the pulp, a radical departure is made from exlsting practices by and useful Improve# the cost of per cent. 4sulfuric acid process both by t y Specification of `Letters Patent'. Patented Aug, 9, 1921,

Application led March 21, 1918. Serial No. 223,694.

particular circumstances tially all, the cyanogen may be freed. yIn f other cases a part of the main combined with the ally desirable to convert salts, `such as cyanides, normal or acid compounds.

cyanogen may remetal, It is usuall alkali and acid cyanates, etc into 4suliites or corresponding A variety of acids may be used for the purpose and the one to be selected will depend chiefly upon the circumstances presented in each case. Sulfuric acid is preferred, and iny some chloric or sulfurous acid or even a substance instances hydro-` giving a very mild acidity may serve the purpose. For instance, a cyanid solution containing silver and copper and approximately a pound of lime per ton of so ution may be successfully treated by adding a ten to neutralize the alkalispresent and `create an acidity of, say, one-tenth of a pound of sulfuric acidv pel-ton of solution;4

in amount sufficient The addition of the'acid frees the cyanogen in the form of hydrocyanic gas, which tends to leave the liquid and diffuse into another gas presentedto it. To removethe hydrocyanic gas from the'liquid, a current of air (or other gas) is accordingly employed, and this is preferably` accomplished by intimately mixing the current of air with the solution in addition to removing the hydrocyanic gas as liberated at the surface of the solution. `This intimate contact of a current. of air with the solution, which may be accomplished, to bubble up throu h the solution, speeds the e agitation and by the quicker separation of the hydrocyanic gas from the liquid. Itmay be complished by placing the solution in a suitable vessel provided with a porous medium in the bottom and creating difference in pressure on opposite sides thereof by means of a vacuum. he operation is accelerated by `the decreased solubllity of the hydrocyanogen in the liquid at reduced pressure and in the event of a leak the gas (which is dangerously poisonous) does not escape, since the leak isinward.- Without attempting an ex-Av for instance, by causing air conveniently acposition o f the chemical reactions, which is unnecessary to the successful. practice of the invention, it may be remarked that the .re-

coveries of cyanogen are, in actual opera` tions using two cubic feet of free air per minute per ton of solution treated, over ninety-five per' cent. of the free alkali cyanids present and of the cyanogen combined with zinc, where zinc`has been used as a precipitant.

The hydrocyanic gas freed by the addition of the acid to the cyanid solution is conducted to an absorbent thereof. In many instances such absorbent will conveniently be the cyanid solution containing free alkali used as the dissolving solution. In other instances, it is more expedient to provide a separate absorbent, as, for instance, caustic soda. The absorption may be mechanically facilitated by passing the gas through a porous diaphragm of a vessel or vessels containing the alkali solution or by passing it through an absorption tower into which the alkali liquor is also fed. In view of the character of the gas, it is desirable to take particular precautlons to secure the absorption of substantially all of it, and it is accordinglypreferable to cause it to pass .through a succession of absorbing mediums. 30

the practice of the invention eliminatesa,

considerable portion of the cost of precipitant and Asubsequent treatment as well as the cost of cyanogen, in addition to promoting lgreater and quicker recovery by enabling the use of stronger solutions. It will be understood that. in metallurgical work specitic conditions vary greatly and the inventionma' be practised without Vperforming all that 1s here recited as available.

The apparatus to`.be employed in practising the process will vary greatly according to the circumstances of a given situation. -In the accompanying drawing is shown a {low-sheet and diagrammatic view f of apparatus which may conveniently beemployed. The crushing of the ore in cyanid solution, followed by additional treatment and filtering, may be conducted as in ordinary practice, the filtered solution being conducted, for convenience, to storage and the tailings or solids to waste. The solution may then be conducted to a vessel A, being conveniently acidifed on -its way to said vessel. The vessel A is provided with a porous portion 4, and the part of the vessel separated off by said porous portion is connected with an inlet, through which air or gas may be drawn into the vessel. The vessel A is connected by a pipe 5 with a vessel B o similar construction, which is connected by a pipe `6 with a vacuum pump 7, capable of creating a partial vacuum or reduced pressure suicient to cause a current of air or' gas to pass through the solutions in vessels A and B, picking up the from the solution in vessel and carrylng it through an absorbent thereof in vessel B. An additional vessel C containing an absorbent ofhydrocyanic gas is preferably, but not necessarily, interposed between vessel B and the vacuum pump 7 as an additional precaution against any escape of the gas. The pipe through which the solution isconducted into the vessel A is preferably provided with a valve 2, controlled by a float 3. The solution is conducted from the vessel A through the pipe 8 to further treatment, as filtering or precipitation, according to known practice. The air or gas carrying the hydrocyanic acid generated by the acidification of the vsolution is drawn through an alkali solution in vessel B Properly to maintain this alkali solution in vessel B, it is connected by means of a pipe provided with a valve, controlled by a ioat, with a storage tank, into whlch cy.- anid,'water and lime or other alkali may be from time to time introduced, as re uired,

` which tank may supply the cyanid so ution to the grinding or crushing mill. A suitable pump 10 is provided to conduct the absorbent solution from the vessel B to the storage tank. It will be understood that the 4particular apparatus shown for purposes of illustration is merel one form of apparatus which may be use in practising the invention and that other forms may also be used in practising the invention as circumstances may indicate. V

, While, for the sake off clearness, the cyanid treated by the invention has been rre- 'erred' to as in a solution and the invention will commonly be practised with the cyanid in that form, it is to be understood that in some cases the cyanid solution from which the cyanogen is recovered will be present as moisture in the residue pulp of decantation. processes or in the cake of filters or other places where the comparative amount of liquid is small, and in such appllcations of the invention it will be convenient to add more liquid to effect its convenient practice.

The invention makes practicable the cyliydrocyanic gas l to those skilled in the art as made desirable by the circumstances of a given situation are contemplated and covered by the following claims l. A cyaniding process comprising dissolving metal in cyanid solution, addingV acid .to said solution to generate hydrocyanic acid gas, connecting the surface of the solution with an alkali absorbent of cyanogen by a 'connection which excludes the atmosphere, admitting air to the bottom of the solution, establishing beyond said absorbent a partial vacuum to draw the air through said solution to pick up the hydrocyanic acid gas therefrom and through said absorbent to'absorb said hydrocyanic acid gas.

2. A process for recovering cyanogen from materials used in cyaniding processes, comprising adding acid to a solution thereof to liberate hydrocyanic acid gas therefrom, subjecting the solution to a vacuum to draw said gas therefrom, and conducting said gas to an absorbent of cyanogen. p

3. A process for recovering cyanogen from materials used in cyaniding processes comprising adding acid to a solution of material comprising cyanogen, liberating hydrocyanic acid gas in the solution, subjecting the solution to a vacuum, permitting another gas-to enter the solution to draw and wash therefrom the hydrocyanic acid gas, andlconducting said gases into contact with an absorbent of cyanogen.

In witness whereof, We have hereunto set our signatures.

LOUIS D. MILLS.

THOMAS B. CROWE. 

